The invention relates to a fuel feed unit for a motor vehicle, with at least one fuel pump fastened to a holding part and intended for sucking in fuel from a baffle arranged in the bottom region of a fuel tank, and with a suction jet pump provided for feeding fuel out of the fuel tank into the baffle and connected to the fuel pump via a supply line.
Such fuel feed units are often used in present-day motor vehicles and are therefore known. The fuel filter, is, as a rule, shaped in the form of a bag and is fastened to an intake connection piece of the fuel pump. The fuel pump is pre-stressed, together with the fuel filter, against the bottom region of the baffle by the holder. A forward-flowline leading from the feed unit to an internal combustion engine of the motor vehicle has a branch for the supply line leading to the suction jet pump. The suction jet pump is usually fastened in the wall of the baffle and serves for ensuring a minimum filling level of fuel in the baffle when the fuel tank is almost empty.
The known fuel feed unit has the disadvantage that it is complicated to mount and the supply line has to be very long for mounting in the fuel tank. However, the result of the supply line having a long length is that, after the fuel pump has been started up, the suction jet pump feeds fuel into the baffle only after a delay. Consequently, when the fuel tank is virtually empty, the fuel pump is often for a short time not supplied with fuel. This may lead to damage to the internal combustion engine or to an exhaust gas catalytic converter.
The problem on which the invention is based is to design a fuel feed unit of the type initially mentioned, in such a way that it is particularly simple to mount and fuel is fed particularly quickly into the baffle after the fuel pump has been started.
This problem is solved, according to the invention, in that the holding part and the suction jet pump form a pre-mountable structural unit.
By virtue of its design, the suction jet pump can be connected to the fuel pump before being mounted in the fuel tank. On account of the invention, it is no longer necessary for the supply line for the suction jet pump to be laid in the fuel tank. The mounting of the feed unit according to the invention, thereby becomes very simple. Another advantage of this design is that the functioning of the fully mounted fuel feed unit can be checked outside the fuel tank. Moreover, the supply line for the suction jet pump can be made very short.
This leads to particularly low flow losses in the supply line and therefore to a particularly low power consumption of the suction jet pump. Since the supply line is of short length, it has a small volume, thus contributing to a particularly short delay in the feed through the suction jet pump after the fuel pump has been started up. Fuel is therefore fed into the baffle virtually immediately after the fuel pump is started up.
According to another advantageous development of the invention, the delay in the operation of the suction jet pump after the fuel pump is started up can be kept particularly small if the supply line of the suction jet pump is led vertically from the delivery side of the fuel pump to the suction jet pump. Furthermore, as a result of this configuration, no gas bubbles can accumulate in the supply line and consequently impair the operation of the suction jet pump.
According to an advantageous development of the invention, the suction jet pump requires a particularly low volume flow of fuel for it to operate if, in the case of a fuel pump with a high-pressure stage and a low-pressure stage, the supply line of the suction jet pump is connected directly downstream of the high-pressure stage, as seen in the direction of flow.
A contribution to further simplifying the mounting of the fuel feed unit according to the invention is made if the holding part is manufactured in one piece with the supply line.
The fuel feed unit according to the invention has a particularly simple design if the holding part for receiving the fuel pump is of pot-shaped design. Moreover, this configuration leads to a particularly simple mounting of the fuel feed unit according to the invention.
The fuel filter, could, for example, be designed in the form of a bag, as in the known fuel feed unit. However, according to another advantageous development of the invention, contamination of the fuel filter is kept particularly low if the fuel filter is arranged in a vertical region of the wall of the holding part. As a result, dirt particles can fall down from the fuel filter after the fuel pump has been switched off.
The fuel feed unit according to the invention is particularly compact if the suction jet pump is arranged directly below the fuel pump. Furthermore, gas bubbles can thereby escape from the supply line very simply.
According to another advantageous development of the invention, the mounting of the holding part, together with the suction jet pump, in the fuel tank becomes particularly simple if the holding part has, in its bottom region, an orifice designed for sucking in the fuel and provided in front of a passage in the baffle for mounting purposes.
The holding part could have, for example, a flange for the connection of the suction jet pump. However, according to another advantageous development of the invention, the holding part can be manufactured, together with the suction jet pump, from plastic in a common injection mold in a particularly cost-effective way if the suction jet pump is manufactured in one piece with the holding part. Mounting of the suction jet pump on the holding part is thereby avoided.
A contribution to further simplifying the mounting of the fuel feed unit according to the invention is made if the holding part has a degassing line for the fuel pump.